The present invention relates to an electronic device, a semiconductor integrated circuit and a data processing system and mainly to a technology effective to be applied to a power supply technology for a battery-driven mobile electronic device.
Standard power supply voltage (such as 3.3 V) has been continuously used for interface between semiconductor chips. On the other hand, pressure resistance of a transistor is decreasing with is improvement of microionization. Thus, internal power supply voltage of a large scale integrated circuit (LSI) directs to be lower voltage for every generation. However, the internal power supply voltage is generally different by each chip in such the LSI. Therefore, when the internal power supply is supplied from a power supply on an implemented board, a number of power supplies equal to a given number of chips must be prepared, which increases in cost of a system and size of an implemented area.
As a technology for overcoming those problems, a method is known including the steps of providing a step-down type switching regulator excluding a smoothing circuit including an inductance and a capacitor on a chip, supplying only a standard power supply voltage Vcc for interface on the semiconductor chip and stepping down the voltage on each chip to generate an internal power supply voltage Vddi. The technology is disclosed in Proceedings of Custom Integrated Circuits Conference, May 1997, pp. 587-590 and International Solid-State Circuits Conference, Digest of Technical Papers, February 1999, pp. 156-157.
According to the conventional technology, the internal circuit on the chip is in a stand-by state (for example, a state where a built-in CPU clock is stopped). Thus, when its load current is significantly small, a power conversion efficiency is reduced extremely. As a result, the switching regulator consumes electric power significantly though only a small amount of power needs to be supplied to the internal circuit. This is because AC power consumed by a switching operation for an output MOSFET, which forms an output pulse within the switching regulator is unnegligibly larger than an output power. Especially in a mobile electronic device, a power loss during such stand-by may reduce a battery lifetime, which is an important performance indicator of the mobile device.
An inventor hereof has realized in Japanese Patent Laid-Open No. 260727/93 and International Patent Publication No. WO 95/09475, through researches of publicly known technologies after the present invention was made, that a power supply had disclosed which combined a switching regulator and a series regulator used them differently trough output current in order to reduce power losses. However, the power supply device monitors the output current in order to switch between them, which appears rational. Yet, in an electronic device such as a microcomputer, currents consumed differ largely between the stand-by state where the central processing unit (CPU) and others perform any operations and an operating state where data processing is performed. Especially, a transition time from the stand-by state to the operating state consumes large current rapidly. Therefore, even when the consumed current is monitored for switching the power supply circuit as described above, voltage and/current required for CPU operations cannot be obtained, which may cause an error operation.